The present invention relates to an exposure apparatus, and, more particularly, to an exposure apparatus that is used in manufacturing a microdevice and transfers a plurality of patterns to a substrate in an overlapping manner, and a method of manufacturing a microdevice, which uses the exposure apparatus.
Conventionally, an exposure apparatus is used in the photolithography step of a microdevice manufacturing process, such as a semiconductor device, a liquid crystal display device, a thin film magnetic head and an image pickup device. The exposure apparatus transfers a pattern formed on a mask, such as a reticle or photomask, to a predetermined area on a substrate, such as a wafer or a glass plate, on which a photosensitive material like a photoresist is coated. The following will describe, as one example, an exposure apparatus for fabrication of semiconductor devices, which transfers a pattern on a reticle to a predetermined shot area on a wafer.
For this type of exposure apparatus, a one-shot exposure type exposure apparatus of a step and repeat system is frequently used. In the step and repeat system, patterns on a reticle are sequentially transferred to individual shot areas on a wafer via a projection optical system while moving the wafer step by step (stepping). Recently, a scanning aligning type exposure apparatus of a step and scan system has been developed. In the step and scan system, a reticle and a wafer are scanned synchronously, thus ensuring projection transfer to a wider area than the exposure field of the projection optical system.
A semiconductor device is formed by stacking multiple circuit pattern layers on a wafer. At the time of executing projection transfer of circuit patterns of the second and subsequent layers to the wafer, it is necessary to accurately align the shot area of a circuit pattern already formed on the wafer with the pattern image of the reticle (i.e., to align the wafer with the reticle).
The conventional exposure apparatus (particularly of the step and repeat system) has a reticle alignment system for detecting a position concerning the reticle and a wafer alignment system for detecting positions concerning wafer marks formed on the individual layers on the wafer. When a reticle is placed in the exposure apparatus, the reticle is positioned in a predetermined position based on the detection result of the reticle alignment system. At the time of transferring the pattern of an N-th layer, for example, the alignment system detects the position of a wafer mark on an immediately previous or (Nxe2x88x921) layer. An offset value to the center of a shot area is added to the positional information of the wafer mark and the shot area is arranged at a reference position such that the center of the shot area coincides with the center of the exposure field of the projection optical system, and the pattern of the reticle is exposed.
When there is a circuit pattern layer on which a wafer mark is not formed, the position of a wafer mark on a layer which is located before the layer having no wafer mark and on which a latest wafer mark is formed (hereinafter called xe2x80x9cimmediately previous mark layerxe2x80x9d) is detected. In the case where alignment is carried out using a wafer mark on the immediately previous mark layer as a reference, however, a slight alignment error (the amount of a positional deviation) that is produced at the time of alignment is added as more layers are stacked on the wafer. This accumulation of errors is problematic in that the positional deviation increases with successive or higher layers.
Further, in a semiconductor device, related patterns should not necessarily be formed on adjoining layers. That is, the N-th pattern and the (Nxe2x88x922) pattern may be electrically connected by a contact hole. In such a case, the amount of positional deviation between the N-th pattern and the (Nxe2x88x922) pattern should be kept to a minimum. According to the conventional exposure apparatus, however, the (Nxe2x88x921) pattern is aligned using the (Nxe2x88x922) pattern as a reference and the N-th pattern is aligned using the (Nxe2x88x921) pattern as a reference. This causes alignment errors among a plurality of layers to be added, so that the alignment precision between related layers is effected.
To overcome this problem, Japanese Unexamined Patent Publication No. 7-249558 and corresponding U.S. Pat. No. 5,532,091 disclose the following alignment method. Assume that a plurality of pattern layers respectively having alignment marks have already been formed on a wafer. When there are patterns in those plurality of patterns which are related to a mark pattern to be transferred next, alignment marks of the related pattern layers are detected. Then, a predetermined exposure area and a mark pattern to be transferred are aligned with each other based on the coordinate values of the alignment marks.
To position individual shot areas on the wafer using the X axis and Y axis that are defined on the wafer surface and perpendicular to each other, a wafer mark for the X axis and a wafer mark for the Y axis are needed for each shot area. According to the aforementioned alignment method, the wafer marks on a plurality of layers are formed to extend two-dimensionally on the surface of the wafer. At the time of executing alignment, therefore, it is necessary to individually measure wafer marks on a plurality of related layers while moving the wafer in the X-axial direction or the Y-axial direction. That is, it is necessary to perform an alignment operation in the X-axial direction or the Y-axial direction for each layer, and further, movement of the wafer is performed during each alignment operation. As apparent from the above, the aforementioned alignment method has a problem such that the time needed for alignment increases, which lowers the throughput.
When the methods of forming the individual pattern layers differ from one another, the cross-sectional shapes of the wafer marks of the individual pattern layers may differ from one another. Such a variation in the cross-sectional shape of a wafer mark impacts an image pickup signal waveform. Further, there is a difference in optical characteristic between the individual pattern layers, such as reflectance, and this difference also causes the image pickup signal waveform to change.
The exposure apparatus measures the position of each wafer mark by observing each wafer mark using the image pickup device of an alignment system and processing the image pickup signal from the image pickup device with a main control system. Here, even though the image pickup signal waveform is varied, the main control system performs the same processing to measure the position of each wafer mark without considering a difference between the signal waveforms. In this case, the measuring result includes an error originated from a variation in signal waveform. This error hinders the accurate alignment of the exposure field of the projection optical system with each shot area.
It is an object of the present invention to provide an exposure apparatus that accurately and quickly transfers mask patterns to a substrate on which a plurality of pattern layers are formed, and a method of manufacturing a microdevice, that uses the exposure apparatus.
According to a first aspect of this invention, there is provided an exposure apparatus comprising a mark-position detecting mechanism which detects positional information of marks on a substrate on which a plurality of layers have been formed, and which transfers a pattern formed on a mask to overlap at least one of the patterns respectively formed on the plurality of layers based on detection results of the mark-position detecting mechanism. The mark-position detecting mechanism includes a one time detection mechanism which simultaneously detecting a first mark formed on a first layer on the substrate and a second mark formed on a second layer different from the first layer on the substrate. A positional information computing device is electrically connected to the one time detection mechanism and computes positional information of the first mark and positional information of the second mark based on the detection results of the one time detection mechanism. The pattern on the mask is aligned with a predetermined exposure area on the substrate based on at least one of the positional information of the first mark and the positional information of the second mark computed by the positional information computing device.
According to a second aspect of this invention, there is provided an exposure apparatus which transfers a pattern formed on a mask to a substrate. The apparatus includes a one time detection mechanism which simultaneously detects a first mark formed on the substrate and a second mark formed on a second surface different from a first surface on which the first mark is formed. A positional information computing device is electrically connected to the one time detection mechanism, corrects a signal corresponding the first mark and a signal corresponding to the second mark, which are detected by the one time detection mechanism, to signals having substantially equivalent waveforms and computes positional information of each mark.
According to a third aspect of this invention, there is provided an exposure apparatus which transfers a pattern formed on a mask to a substrate. The apparatus includes a one time detection mechanism which simultaneously detects a first mark formed on the substrate and a second mark formed on a second surface different from a first surface on which the first mark is formed. A processing unit is electrically connected to the one time detection mechanism and processes a signal corresponding the first mark and a signal corresponding to the second mark, which are detected by the one time detection mechanism, under processing conditions different from each other.
According to a fourth aspect of this invention, there is provided a method for detecting positional information of marks on a substrate on which a plurality of layers have been formed and for transferring a pattern formed on a mask to overlap at least one of the patterns respectively formed on the plurality of layers based on the positional information of marks. First, a first mark formed on a first layer on the substrate and a second mark formed on a second layer different from the first layer on the substrate are simultaneously detected. Then, positional information of the first mark and positional information of the second mark is computed based on signals obtained by the simultaneous detection step. The pattern on the mask is aligned with a predetermined exposure area on the substrate based on at least one of the computed information of the first mark and the computed positional information of the second mark.
According to a fifth aspect of this invention, there is provided an exposure method for transferring a pattern formed on a mask to a substrate. First, a first mark formed on the substrate and a second mark formed on a second surface different from a first surface on which the first mark is formed are simultaneously detected. Then, a signal corresponding the first mark and a signal corresponding to the second mark, which are detected by the one time detection mechanism, are corrected to signals having substantially equivalent waveforms to compute positional information of each mark.
According to a sixth aspect of this invention, there is provided an exposure method for transferring a pattern formed on a mask to a substrate. First, a first mark formed on the substrate and a second mark formed on a second surface different from a first surface on which the first mark is formed are simultaneously detected. Then, a signal corresponding the first mark and a signal corresponding to the second mark, which are detected by the one time detection mechanism, are processed under processing conditions different from each other.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.